Method and apparatus for pressure cast coating



Jan. 3, 1967 R. c. WILLIAMS 3,296,014

METHOD AND APPARATUS FOR PRESSURE CAST COATING 2 Sheets-Sheet 1 FiledMarch 4, 1964 Jan. 3, 1967 R. cv WILLIAMS 3,296,014

METHOD AND APPARATUS FOR PRESSURE CAST COATING 2 Sheets-Sheet 2 FiledMarch 4, 1964 FIG. 3

United States Patent 3,296,014 METHOD AND APPARATUS FOR PRESSURE CASTCDATING Robert C. Williams, 9902 River Road, Richmond, Va. 23229 FiledMar. 4, 1964, Ser. No. 349,219 12 Claims. (Cl. 11764) This inventionrelates to a method and apparatus for cast coating paper. Morespecifically, this invention relates to an improved method and apparatusfor pressure cast coating paper webs in a very simple and expeditiousmanner.

Since the inception of cast coating (US. Patent 1,719,166) numerousimprovements have been made in the art. Many of these improvements havebeen directed to solution of the problem known as blowing which iscaused by vaporization of the liquid component in the coatingformulation whereby the coating is forced away from the heated dryerdrum before it is cast. For this reason, early cast coating operationswere limited to the use of temperatures less than 212 F. A significantrecent improvement in the art of cast coating paper wherebytemperature-s greater than 212 F. can be employed is that known aspressure cast coating, e.g. see US Patent 3,110,612. That techniquecomprises heating a wet coated paper web to the vaporization temperatureor above of the volatile component of the coating formulation whileconcomitantly compressing the paper web by pressure belt meanssufficient to maintain the paper Web in contact with the castingsurface. By operating in this manner, viz. employing operatingtemperature-s greater than 212 F., greater production rates areachieved. While elegant results are realized by way of the lattertechnique, a method and means for pressure cast coating withoutnecessitating the use of pressure belt means would be a welcomedcontribution to the art.

An object of this invention is to provide a method for pressure castcoating which does not require the use of belt pressure means.

Another object of this invention is to provide an appara tus forpressure cast coating which does not require belt pressure means forcasting a coating upon the paper web.

A more specific object of the instant invention is to provide a methodand apparatus for pressure cast coating paper webs without pressurizingthe paper web itself during the casting operation whereby belt pressuremeans are dispensed with.

These and further objects will come to light as the discussion proceeds.

FIGURE 1 depicts one embodiment of the apparatus of this inventionwherein the process of this invention can be practiced.

FIGURE 2 is a more detailed arrangement of another embodiment of theapparatus of this invention.

FIGURE 3 depicts yet another apparatus arrangement wherein the processof this invention can be practiced.

It has now been found that high temperature pressure cast coatingutilizing a hardenable coating formulation comprising a volatile liquidcomponent can be conducted by contacting a wet coating of said coatingformulation applied to a paper web with a casting surface; heating saidcoating to a temperature above the vaporization temperature of saidvolatile liquid component so as to generate vapors thereof; whilesimultaneously compressing said coating on said web against said heatedcasting surface by pressurized air until said coating is cast; andthereafter releasing said cast coated web from said heated castingsurface by releasing the air pressure and allowing any moisture in theweb to flash therefrom. Operating pursuant to this method prevents thevapors generated in the coatice ing from blowing the oating away fromthe heated casting surface. The air pressure uniformly presses betweenthe pores in the sheet so as to keep the coating tightly pressed againstthe drum. Consequently, operating temperatures exceeding 212 F. can beemployed. The gen erated vapors are forced to flow away from the castingsurface toward and through the base web. Moisture re maining in the baseweb is removed by flashing upon exit of the coated web from the highpressure casting zone.

Among the chief advantages and features of the instant invention is thata pressure belt means as heretofore employed in the art of pressure castcoating is dispensed with. This results not only in equipment savings,but additionally in cost of operation since there are less parametersand equipment for the machine operator to control. Moreover, since thebase sheet is porous, air pressure is applied to the coating itself thuseliminating transfer of sheet and felt imperfections to the coating whenpressure is applied via belt.

The apparatus of the present invention wherein the above method can bepracticed is that as shown in the embodiments depicted in the drawings.In FIGURE 1, a paper web 10 to be cast coated is conveyed over rollers11 and 12 into position to receive a wet coating of the coatingformulation 13 contained in means 14. The coating formulation 13 isapplied to the web 10 by the applicator rolls 15 and 16. The wet coatingon the web 10 is smoothed out and excess removed therefrom by the airknife doctor 17, residual coating material being collected in means 18and recycled for subsequent reuse. The wet coated paper web is then fedto the casting unit which comprises the dryer drum 19. The drum 19 has apolished chromium casting surface over which the web 10 is conveyed andpositioned by the conveyance means 20 and 21.

The air pressurizing means 22 is constructed so as to form a shroud andessentially air-tight compartment with respect to the casting or dryerdrum means 19. A certain amount of air leakage from the casting zonedefined by the drum means 19 and the air pressurized means 22 isdesirable since it prevents buildup of moisture within the system. Airunder pressure is injected into the air pressurizing means 22 bysuitable inlet ports, for example at 23 and 24.

Upon exit from the high temperature pressure casting zone, moisture inthe cast coated web 10 will flash at the exit nip 25. Such flashing doesnot disrupt the coating since it is fully cast and strong enough at thispoint to resist the forces that come into play. The cast coated web 10is then fed off the drum means 19 over the roller 26 to windup.

The design of the air pressurizing means can vary considerably withoutdeparting from the true spirit of this invention.

A more detailed design of a similar embodiment of the apparatus of thisinvention is that as depicted in FIGURE 2. The paper web 30 is fed intoposition to receive a coating by the applicator rollers 32 and 33 of thecoating formulation 34 contained Within means 35. The wet coating on theweb 30 is smoothed out and excess material removed by the air knifedoctor 36, the residual material being collected in means 37 andrecycled for subsequent reuse.

The Wet coated web is then fed to the casting unit which comprises thedryer drum 38. The Wet coated web 30 is coveyed and positioned over thecasting surface of the drum 38 by the conveyor means comprising therollers 39 and 40.

The dryer or casting drum 38 further comprises steam injection anddistribution means 41 and condensate removal means 42. The wet coatedweb 30 is compressed upon the casting surface of the dryer drum 38 bypres- {B surized air fed through ports 43 and 44 to the air pressurizingmeans 45. The inside peripheral surface 46 of the air pressurizing means45 is foraminous.

The air injected into the member 45 passes through the foraminoussurface 46 and the paper Web 30 and thereby compresses the coating onthe paper web 30 upon the casting surface of the drum means 38. Theclearance between the foraminous surface 46 and the casting surface ofthe drum means 38 is very small so as to minimize air usage. Upon exitfrom the high temperature pressure casting zone, most of the moistureabsorbed by the paper W603i) flashes therefrom at the exit nip 47. Thefinal product cast coated paper web 30 is then conveyed to windup.

In the apparatus arrangement of FIGURE 3, the paper web 50 havingpreviously received a wet coating is fed to the heated casting drum 51.The coating on the web 50 is pressed against the circumferential surfaceof the drum by the air pressure means comprising the rollers 52, 53, and54. The pressure means further comprises the end closure plates means 55(one on each side) which together with the rollers 52-54 form anessentially air tight high pressure and temperature casting chamber orzone. Pressurized air is injected into the zone through the inlet port56. The rollers 52, 53, and 54 are provided with suitable means 57, 58,and 59 respectively (e.g., a hydraulic system) for urging the rollerstoward each other and the drum 51 so as to provide the desiredessentially air tight chamber. The chamber defined as above is notintended to be fully air tight inasmuch as vapors of moisture generatedduring the casting operation are preferably allowed to escape. However,the vapors can be removed via suitable exhaust means.

Upon exit from the high temperature pressure casting zone, most of themoisture absorbed by the paper Web 50 flashes therefrom at the exit nip60. The web can be further dried upon exit from the casting zone byallowing it to remain in contact with the heated drum 51 for anadditional period of time as shown in the drawing. It is to beunderstood that the number of rollers and their positions with respectto the dryer drum can vary without departing from the spirit of thisinvention.

In producing cast coated paper pursuant to the practice of thisinvention, it is preferred to operate Within a temperature range of fromabout 220 F. to about 350 F., especially within about 240 F. to 260 F.Moreover, it is preferred to exert a pressure upon the web within therange of from about psi. to about 50 p.s.i., particularly from aboutp.s.i. to about 35 p.s.i. Operating under these conditions, cast coatedpaper having optimum properties is produced at lowest cost.

A typical coating formulation for use in the instant invention comprisesa pigment, an adhesive, and water. The pigment can be clay, blanc fixe,satin white, talc, calcium carbonate, titanium dioxide, and the like,plus mixtures thereof. Suitable adhesives are casein, glue, starches,gums, alpha-proteins, and the like, as well as mixtures thereof. It isunderstood of course that other materials can be added, such as waxes;carnauba, beeswax, and the like; water proofing agents: shellac,formaldehyde, and the like; as well as special materials such as: dyes,powdered metals, defoamers, wetting agents, release agents, and thelike. The coating formulation is preferably applied at about 8 to about25 pounds per 3000 square feet of base stock.

The following examples are presented wherein all parts are by weightunless otherwise specified.

Example 1 Base stock Dryer temperature300 F. Air pressure33 p.s.i.g.Results-very smooth finish and high gloss characteristic of castcoatings.

Example II Base stock 18 mil thick uncalendered board 7 lbs./ream/mildensity 60 percent kraft and 40 percent groundwood Coating20 lbs/ream,composed of parts clay, 18 parts protein and sufiicient water to make 50percent solids. Dryer temperature350 F. Air pressure-6O p.s.i.g.Resultsultra smooth finish and high gloss characteristic of castcoatings.

Example III Base stock- 28 mil thick uncalendered board 7 lbs./ream/mildensity 60 percent kraft and 40 percent groundwood Coating-2 lbs/ream,oxidized starch from 20 percent solids aqueous solution. Dryertemperature300 F. Air pressure33 p.s.i.g. Resultsvery smooth finish andhigh gloss characteristic of cast coatings.

Example IV Base stock 23 mil thick calendered board 7 lbs./ream/mildensity 100 percent kraft Coating20 lbs/ream, composed of 100 partsclay, 12 parts protein, and 6 parts latex (butadiene-styrene) andsufficient water to make 55 percent solids. Dryer temperature-300 F. Airpressure-63 p.s.i.g. Resultsvery smooth finish and high glosscharacteristic of cast coatings.

Example V Base stock 18 mil thick uncalendered board 7 lbs./ream/mildensity 60 percent kraft and 40 percent groundwood Coating-3 lbs/ream,oxidized starch from 20 percent solids aqueous solution. Dryertemperature-260 F. Air pressure18 p.s.i.g. Resultsvery smooth and glossyfinish.

Cast coated paper produced as above is found to have not only an elegantappearance, but additionally excellent mechanical properties inasmuch asbonding between the coating and the base web is exceptionally good.-

I claim:

1. A high temperature pressure cast coating method utilizing ahardenable coating formulation comprising a volatile liquid component,said method comprising:

(1) contacting a wet coating of said coating formulation, applied upon apaper web, with a casting surface,

(2) heating said coating to a temperature above the vaporizationtemperature of said volatile liquid component so as to generate vaporsthereof, while simultaneously (3) compressing said coating on said webagainst said heated casting surface by pressurized air until saidcoating is cast, and thereafter (4) releasing said cast coated web fromsaid heated casting surface by releasing said air pressure and allowingmoisture in said web to flash therefrom.

2. The process of claim 1 further characterized in that said castingsurface is maintained at a temperature within the range of from about220 F. to about 350 F.

3. The process of claim 1 further characterized in that said castingsurface is maintained at a temperature within the range of from about240 F. to about 280 F.

4. The process of claim 1 further characterized in that said coating onsaid web is compressed against said heated casting surface at a pressurewithin the range of from about 5 p.s.i.g. to about 50 p.s.i.g.

5. The process of claim 1 further characterized in that said coating onsaid web is compressed against said heated casting surface at a pressurewithin the range of from about p.s.i.g. to about 35 .p.s.i.g.

6. The process of claim 1 further characterized in that said coatingformulation comprises a pigment, an adhesive, and water.

7. The process of claim 1 further characterized in that said coatingformulation is applied at about 8 to about pounds per 3000 square feetof base stock.

8. A high temperature pressure cast coating method utilizing ahardenable coating formulation comprising a volatile liquid componentfor cast coating a continuous and moving paper web, said methodcomprising:

(1) applying a wet coating of said coating formulation to said movingpaper web,

(2) contacting said coating with a heated casting surface, said surfacebeing at a temperature sufficient to vaporize said volatile liquidcomponent,

(3) compressing said coating against said heated casting surface bypressurized air suflicient to force said vapors through said coating,

(4) maintaining said heat and said pressure until said coating is cast,and thereafter (5) releasing said cast coated paper web from saidcasting surface in a reduced pressure zone whereby any moisture in saidpaper web is allowed to flash therefrom.

9. A high temperature pressure cast coating apparatus for casting ahardenable coating formulation comprising a volatile liquid componentupon a continuous and moving paper web, said appaartus comprising:

(1) rotatably mounted casting drum means having a circumferentialcasting surface,

(a) said drum means being further defined in that it further comprisesheating means whereby the casting surface of said drum means is heatedto a temperature sufiicient to cast said coating formulation upon saidpaper Web,

(2) means for conveying said wet coated paper web into contact with thecasting surface of said drum means, the extent of contact between saidwet coated paper web and the casting surface of said drum means beingprescribed by the position of said conveying means with respect .to saiddrum means, and

(3) pressurizing means positioned relative to said rotatably mounteddrum means so as to form an enclosed casting chamber, and

(a) said pressurizing means further defining means for injecting apressurized gas into said chamber whereby said coating on said web ispressed against the circumferential surface of said drum means as saidWeb passes through said casting chamber.

10. The apparatus of claim 9 further defined in that said pressurizingmeans has a foraminous surface in juxtaposition to said paper Web.

11. A high temperature pressure cast coating apparatus for casting ahardenable coating formulation comprising a volatile liquid componentupon a continuous and moving paper web, said apparatus comprising:

(1) rotatably mounted casting drum means having a circumferentialcasting surface (a) said drum means being further defined in that itfurther comprises heating means whereby the casting surface of said drummeans is heated to a temperature sufficient to cast said coatingformulation upon said paper web,

(2) air pressurizing means comprising (a) multiple roller meansrotatably mounted in series contact with each other, the first and lastrollers of which are positioned relative to said drum means so as to bein contact with said paper web,

(b) closure means in combination with said roller means and said drummeans so as to form an enclosed casting chamber, and

(c) means for injecting a pressurized gas into said casting chamberwhereby said coating on said Web is pressed against the circumferentialsurface of said drum means as said web passes through said castingchamber.

12. The apparatus of claim 11 further defined in that said multipleroller means comprises three roller means.

3,110,612 11/1963 Gottwald et a1. 11764 MURRAY KATZ, Primary Examiner,

9/1947 Grupe 11764I

1. A HIGH TEMPERATURE PRESSURE CAST COATING METHOD UTILIZING AHARDENABLE COATING FORMULATION COMPRISING A VOLATILE LIQUID COMPONENT,SAID METHOD COMPRISING: (1) CONTACTING A WET COATING OF SAID COATINGFORMULATION, APPLIED UPON A PAPER, WEB, WITH A CASTING SURFACE, (2)HEATING SAID COATING TO A TEMPERATURE ABOVE THE VAPORIZATION TEMPERATUREOF SAID VOLATILE LIQUID COMPONENT SO AS TO GENERATE VAPORS THEREOF,WHILE SIMULTANEOUSLY (3) COMPRESSING SAID COATING ON SAID WEB AGAINSTSAID HEATED CASTING SURFACE BY PRESSURIZED AIR UNTIL SAID COATING ISCAST, AND THEREAFTER (4) RELEASING SAID CAST COATED WEB FROM SAID HEATEDCASTING SURFACE BY RELEASING SAID AIR PRESSURE AND ALLOWING MOISTURE INSAID WEB TO FLASH THEREFROM.